Astronomers find planet in two-star system

Sunday, November 3, 2002

By Alexandra Witze, The Dallas Morning News

DALLAS -- University of Texas astronomers have confirmed that a planet orbits one of a pair of stars 45 light-years (260 trillion miles) away. It is the first discovery of a planet in a binary star system where the two stars orbit each other closely.

Such binary systems are common in the galaxy.

"When you look at the stars in the sky, every other one of them is a double star or multiple star," Canadian astronomer Gordon Walker said.

Planets have been found in binary star systems before, but in those cases the two stars were separated by a distance at least 100 times greater than in this case.

If a planet can form in a close binary system, without getting tossed out of orbit by the secondary star, then planets might be more common in the universe than previously believed, Walker said.

William Cochran of the University of Texas-Austin led the research team.

The star is Gamma Cephei, the third-brightest star in the constellation Cepheus the King. Gamma Cephei has a dim companion star that orbits from 1 billion to 3 billion miles away; at most, that places the two stars as far apart as the sun and Neptune.

The newfound planet orbits Gamma Cephei at an average distance of 200 million miles, or about twice the distance between the sun and the Earth. The planet is nearly twice as massive as Jupiter and takes about two years to go around its star.

Gamma Cephei is the brightest star other than the sun known to have a planet, Cochran said.

Astronomers don't know whether the planet might have formed around Gamma Cephei, or whether it might have been captured from elsewhere in space. But its near-circular orbit suggests that it may have formed in place, Walker said.

And that could mean Gamma Cephei's planet, or any moons it may have, would be good places to search for extraterrestrial life. It could be at the right distance for water -- considered a prerequisite for life -- to exist without boiling away or freezing.

Walker published a paper in 1988 suggesting that Gamma Cephei might have a planet.